1. Field of the Invention
The present invention relates to an information recording and read system of the type having scanning means for scanning a track on a record carrier of an inscribable type for the purpose of recording and reading information thereon. The scanning speed during recording substantially corresponds to the scanning speed during reading. A recording device records the information in the track at the scanning location, and a read device reads the information which has been recorded in the track at the scanning location. The invention also relates to the recording device and the read device of such a system.
2. The Related Art
An optical recording and read system of the aforesaid kind is known from Applicant's European patent document EP-A 0,325,330, which corresponds to U.S. Pat. No. 4,999,825. According to that patent, for the purpose of recording and/or reading, the track of a disc-shaped optical record carrier is scanned by a radiation beam which is focused on the record carrier.
In order to enable the recording and read process to be optimized, various servo arrangements are needed for scanning control. For example, optical recording and read devices include, inter alia, a tracking control for keeping the radiation beam on the track, a focus control for keeping the radiation beam focused on the record carrier, and a speed control for controlling the scanning speed. Disturbances which affect the servo systems are mainly disturbances caused by imperfections of the record carrier, such as, for example, an eccentric position of the center of rotation, non-circularity of the tracks and non-flatness of the record carrier. The width of the frequency spectrum of these disturbances is a direct function of the scanning speed, so that optimum adaption of the servo system to such disturbances depends strongly on the scanning speed.
This dependence constitutes a problem when a recording and read device processes a digital signal, for example, a digitized audio or video signal, whose bit rate, for example, as a result of another digitizing method or data compression, is lower than that for which the recording device was designed. Maintaining the scanning speed at the original value during recording then has the drawback that the information density on the record carrier, as represented by the required length per bit, will be substantially reduced and so the available storage capacity of the record carrier is only partly utilized. Conversely, reducing the scanning speed has the drawback that the operation of the servo systems will no longer be optimal.